The present invention relates generally to a method for determining a blistered film in layered films and, more particularly, to a method for identifying which film of the layered films has blistered. For example, blisters may be formed in the layered films when a semiconductor wafer having a plurality of kinds of layered films is subjected to heat treatment during a process for producing a semiconductor device.
As the scale of integration in semiconductor devices increases and the structure thereof becomes more complicated, semiconductor devices are constituted by more and more kinds of films such as insulating films, conductive films, and metal films. In addition, the thickness of each film has been extremely reduced. In a typical process for producing semiconductor devices, many kinds of films are layered one on top of another in a predetermined sequence. At a predetermined stage of the production process, heat treatment is often effected on a semiconductor wafer having the layered films. In this case, as the result of heat treatment, a blister is often formed in the layered films because of differences in thermal expansion coefficients among the various films, or because of the discharge of gases contained therein. The presence of such a blister in a layered film not only makes it difficult to form a fine pattern, but also causes electrical defects or failures such as broken wires and short-circuits. In addition, this may produce adverse influences such as a reduction in the product yield of semiconductor devices or a reduction in the reliability thereof.
Accordingly, in a case where a blister is formed in layered films, determining which film of the layered films is blistered has become increasingly important in acquiring information relative to improvements in the structure, film material, production methods and so forth of semiconductor devices.
In a prior art method for identifying a blistered film in layered films, a semiconductor wafer is cut, and the cut cross section thereof is observed by means of an optical microscope or scanning type electron microscope, to thereby determine which film of the layered films has blistered.
However, the above-described prior art method for determining a blistered film involves the following disadvantages. In the prior art method, it is extremely difficult to cut a semiconductor wafer so as to slice a blister exactly in a crosswise direction thereof. In addition, since the size of a blister formed in a film on a semiconductor wafer is usually quite small, it is very rare for a single cutting operation to provide a sample including a blister which is cut exactly crosswise. Therefore, a desired sample cannot be obtained until a multiplicity of cutting operations are repeated and hence a significant number of semiconductor wafers are wasted. Accordingly, such a method for determining a blistered film by cutting a semiconductor wafer is unstable, unreliable, complicated and uneconomical.